This invention is directed generally to polysiloxane hydrolyzates, and is an improvement over existing methods of neutralizing and/or purifying polysiloxane hydrolyzates. In particular, hydride functional linear, branched and/or cyclic polysiloxane (≡Si—H) hydrolyzates, and linear, branched and/or cyclic polydialkylsiloxane hydrolyzates such as polydimethylsiloxane (PDMS) hydrolyzates, are more efficiently neutralized and purified according to the invention.
The hydrolysis of chlorosilanes is known in the art, and reference may be had to U.S. Pat. No. 4,382,145 (May 3, 1983), and pending U.S. patent application Ser. No. 10/958,768, filed on Oct. 5, 2004, entitled “Hydrolysis of Chlorosilanes”, that represent the state of the art. The '145 patent and the pending application are directed to general processes for producing polysiloxane hydrolyzates from chlorosilanes. U.S. Pat. No. 5,075,479 (Dec. 24, 1991) describes a hydrolysis process for producing PDMS hydrolyzates, whereas U.S. Pat. No. 5,493,040 (Feb. 20, 1996) relates to a hydrolysis process for producing hydride functional polysiloxane hydrolyzates.
Typically, hydrolyzates containing cyclic and linear hydride functional polysiloxanes are obtained by hydrolyzing CH3SiHCl2 and (CH3)3SiCl. The hydrolyzate is neutralized with sodium bicarbonate to remove trace levels of chlorine based species, particularly chloride ions in the form of hydrochloric acid (HCl) and then used in the preparation of higher molecular weight hydride functional polysiloxane polymers. Hydrolyzates containing cyclic and linear PDMS are obtained by hydrolyzing (CH3)2SiCl2 with or without either (CH3)3SiCl or an endblocking oligomer such as (CH3)3SiO[(CH3)2SiO]0-10. The hydrolyzate is typically neutralized with sodium bicarbonate to remove trace chlorine based species such as HCl and then used in the preparation of higher molecular weight polydimethylsiloxane polymers. U.S. Pat. No. 5,276,173 (Jan. 4, 1994) describes the removal of ionic chloride from hydroxyl-terminated siloxane compounds by contacting the siloxane with a molecular sieve material.
Quite unexpectedly, it has been discovered that the use of carbon instead of sodium carbonate or sodium bicarbonate for neutralizing and purifying polysiloxane hydrolyzates is beneficial in that it produces a reduction in the cycle time normally needed for neutralization and purification of these hydrolyzates. In the case of PDMS hydrolyzates, it was also found to reduce the viscosity drift of the resulting PDMS polymers. This was particularly surprising as carbon manufacturers were of the opinion that carbon should not be appropriate for this purpose.